Passage
The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne⁻ → X(0) , E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.
Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.
Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C.
-Iodine reacts with ClO₃⁻ under acidic conditions according to the reaction shown below.5 ClO₃⁻ + 3 I₂ + 3 H₂O → 5 Cl⁻ + 6 IO₃⁻ + 6 H⁺Does I₂ act as the oxidizing agent or reducing agent in the reaction?

Question

Passage
The tendency of a chemical species to undergo reduction during an electrochemical reaction is indicated by the standard potential E° for the reaction. As represented generally by Reaction 1, E° measures the potential Z at which element X with oxidation number N accepts N electrons and is reduced to its elemental state.X(N) + Ne⁻ → X(0) , E° = Z voltsReaction 1In a galvanic cell, E° > 0 indicates a spontaneous reaction. Therefore, chemical species with higher positive E° values are reduced more easily than those with lower E° values.Using E° as a basis of comparison, the relative thermodynamic stabilities of different chemical species involving the same element at different oxidation states can be presented graphically using a Frost diagram. For a series of compounds containing element X, a Frost diagram plots the value of NE° for each compound against the corresponding oxidation number N of element X within the species. Frost diagrams for several species containing manganese or chlorine are shown in Figure 1.

Figure 1 Frost diagrams for manganese and chlorineOn a Frost diagram, NE° is proportional to the standard Gibbs free energy ΔG° according to the relationshipΔG° = −FNE° = −nFE°Equation 1where n is the number of moles of electrons transferred during the electrochemical process and F is the Faraday constant. Free energy considerations also show that a species is prone to disproportionation if its position on the Frost diagram lies above a line connecting the points of two adjacent species, as seen for species B in Figure 2.

Figure 2 General Frost diagram for an element forming species A, B, C, and D.The slope of a line segment joining two species on a Frost diagram is equal to the standard reduction potential for the couple. A greater slope indicates a higher corresponding reduction potential. As a result, in Figure 2, the reduction potential for B to A is lower than that for D to C.
-Iodine reacts with ClO₃⁻ under acidic conditions according to the reaction shown below.5 ClO₃⁻ + 3 I₂ + 3 H₂O → 5 Cl⁻ + 6 IO₃⁻ + 6 H⁺Does I₂ act as the oxidizing agent or reducing agent in the reaction?

Quizplus · Accepted Answer

11ecba2d_1223_7125_a3bf_f3d51d38e6c4_MD0008_00 In an electrochemical reaction, oxidation and reduction always occur simultaneously. The electrons lost by the atom that is oxidized are gained by another atom that is reduced. As a result, the chemical species containing the atom being oxidized is the reducing agent that causes reduction in another atom by giving up the electrons involved in the reduction in the other atom. Conversely, the species with an atom that is reduced functions as the oxidizing agent that causes oxidation by taking electrons from (oxidizing) another atom. In the given reaction, the chlorine atom in ClO₃⁻ is reduced while the iodine atoms in I₂ are oxidized. This can be determined by examining the changes in the bonds to oxygen between the species, by assigning oxidation numbers, or by reading the oxidation numbers for chlorine directly from the Frost diagram in the passage (Figure 1). During the reaction, the chlorine atoms lose bonds to oxygen and have a decrease in oxidation state from +5 to −1. In contrast, the iodine atoms gain bonds to oxygen and have an increase in oxidation state from 0 to +5. Therefore, I₂ acts as the reducing agent by giving up electrons and causing ClO₃⁻ to be reduced. In the process, I₂ itself gets oxidized because it is losing the electrons. (Choices A and C) Oxidizing agents cause oxidation in another compound. I₂ cannot be the oxidizing agent in the given reaction because the chlorine atom in ClO₃⁻ is reduced. It is the I₂ itself that is oxidized. (Choice D) Reducing agents cause reduction in another compound. Because I₂ is the reducing agent in the given reaction, ClO₃⁻ is reduced rather than oxidized. Educational objective: A reducing agent is a chemical species that gets oxidized and causes reduction in another atom in the process, whereas an oxidizing agent is a chemical species that gets reduced and causes oxidation in another atom as a result. Oxidation and reduction always occur together.

Passage The Tendency of a Chemical Species to Undergo Reduction During